After a drug is administered to a living body, it reaches an affected site and exerts its pharmacological effects at that affected site, thereby exerting its therapeutic effects. On the other hand, even if the drug reaches tissue other than the affected site (that is, normal tissue), it will not be therapeutic, but also cause adverse reactions.
Therefore, how to guide the drug to the affected site is important in terms of therapeutic strategies. A technique to guide the drug to the affected site is called drug delivery, which has been actively studied and developed recently. This drug delivery has at least two advantages.
One advantage is that a sufficiently high drug concentration can be obtained at the affected site tissue. Pharmacological effects will not be seen unless the drug concentration at the affected site is a constant value or more. This is because the therapeutic effects cannot be expected if the concentration is low. The second advantage is that the drug is guided to only the affected site tissue and will not be guided to the normal tissue unnecessarily. As a result, adverse reactions can be inhibited.
Such drug delivery is most effective for a cancer treatment by anti-tumor agents. Most anti-tumor agents inhibit the cell growth of cancer cells which divide actively, so that the anti-tumor agents will also inhibit the cell growth of even the normal tissue in which cells divide actively, such as bone marrow, hair roots, or alimentary canal mucosa.
Therefore, cancer patients to whom the anti-tumor agents are administered suffer adverse reactions such as anemia, hair loss, and vomiting. Since such adverse reactions impose heavy burdens on the patients, the dosage needs to be limited, thereby causing a problem of incapability to sufficiently obtain the pharmacological effects of the anti-tumor agents.
So, it is expected to inhibit the adverse reactions and perform the cancer treatment effectively by guiding the anti-tumor agents to the cancer cells by means of the drug delivery and making the anti-tumor agents exert the pharmacological effects intensively on the cancer cells.
The applicant of the present application suggested an iron-salen complex as an example of such anti-tumor agents. Since this iron-salen complex is magnetic itself, it can be guided to the target affected site tissue by means of an external magnetic field without using a magnetic carrier. (See, for example, Patent Literature 1).